1. Field of the Invention
This invention relates to an ink jet printer for emitting ink droplets to record letters and images.
2. Description of the Related Art
The ink jet printer is a type of printer for recording letters and images formed from ink dots arriving on a recording medium, such as, paper after being emitted as droplets of ink from fine nozzles arrayed in the printer head. The ink-jet printer is characterized by having a high recording speed, a low recording cost and further easily performing color printing.
Printer heads in the ink-jet printer of the related art come in two types: a so-called serial head shorter than the page width of printing paper, and a so-called line head having almost the same length dimensions as the page width of printing paper. As methods for emitting the ink droplets there are the piezo method utilizing a piezoelectric element, and a thermal method utilizing a thermal (or heat-emitting) element.
The line head method mentioned above, unlike the serial head, is characterized by not requiring a drive means, such as a motor, to move in the direction of the page width when recording, so the printer chassis can be made compact and costs can be reduced.
Compared to the piezo method, the thermal method is characterized in that increasing the number of drive elements and placement density in order to emit the ink droplets is relatively easy, so the thermal method is ideal for use with the line head method. This invention therefore proposes an ink-jet printer comprising a thermal-type line head.
Compared to the piezo method, the thermal method has the disadvantages of low energy efficiency and large power consumption during recording. To eliminate these disadvantages, the plurality of thermal elements, such as employed in thermal-type serial heads, must be apportioned into a certain number of blocks, and a time-division drive method for sequentially driving each thermal element in a block on shared time also must be applied to each block.
The ink-jet printer of the related art also generally utilized digital image processing, such as the so-called dither method, and an error diffusion method to express print tones. However, these methods essentially utilize a plurality of dots to express the print tones so that the actual resolution of the print is low, and the dots have a grainy, rough appearance to the human eye that reduces the image quality. The dot size must therefore be made smaller and the dot placement density must be increased in order to improve the printing resolution and image quality.
Of these problems, the dot size in both the thermal-type line head and the serial head can be made smaller by reducing the size of the thermal elements, the diameter of the nozzles and the volume of the chamber to reduce the volume of the ink particles being emitted.
However, compared to serial heads, the problem of dot placement density is difficult to eliminate in thermal type line heads. This problem is due to the fact that while the serial head will have several hundred nozzles, the line head will require several thousand nozzles in the case for instance of an A4 sheet of paper. The large number of nozzles not only greatly reduces the production pace of nozzle manufacture, but also creates problems because of the large scale increase in head driver circuits and the related higher costs and reliability.
Therefore, a method using the so-called tiling method is utilized which employs an array of a plurality of head chips containing a specified number of nozzles.
Line heads utilizing this tiling method are comprised for instance as shown in FIG. 19.
In FIG. 19, a line head 1 is comprised of a plurality of head chips 2 (five head chips 2 are shown in the figure) each installed with a specified number of nozzles (not shown in drawing) connected so as to be arrayed in a straight line.
As also shown in FIG. 19, the nozzles arrayed in a straight line and the head chips 2 comprising the nozzle 1 are subdivided into blocks 3 and the nozzle of each block is driven in sequence by time-division. Each head chip 2 is therefore also comprised of a drive circuit 4 containing drive elements such as the aforementioned thermal elements. These drive circuits 4 respectively correspond to a time-division driven block 3.
Here, each drive circuit 4 is comprised of a thermal element 4a and a switching element 4b as shown in FIG. 21. When the switching element 4b is turned on by the drive signal, drive current flows in the thermal element 4a so that the thermal element 4a emits heat and emits ink from the corresponding nozzle.
The plurality of nozzle units of each block 3 are in this way sequentially time-division driven by the corresponding drive circuit 4 so that ink is emitted.
However, in a line head 1 configured by tiling of this kind, the above described number of time-division drive phases or in other words, the number of nozzles for each block is set regardless of the number of nozzles for each head chip 2.
The wiring of the drive circuit 4 corresponding to the drive element for emitting ink from each nozzle is therefore different and the wiring for each head chip 2 in the entire line head 1 becomes complicated, and the configuration of the drive circuits 4 for each head chip 2 is therefore different.
One block is comprised of 16 nozzles as shown in FIG. 20, and each head chip 2 has 15 nozzles. When the number of time-division drive phases is 8, the first head chip 2A is comprised of a drive circuit 4 for driving nozzles from phase No. 1 through 15 as shown in FIG. 21A. A second head chip 2B contains a drive circuit 4 for driving the nozzle for phase No. 16 of the first block, and nozzles for phase No. 2 through 14 of the second block, as shown in FIG. 21B.
However, the above configuration requires fabricating multiple types of head chips 2A, 2B containing different types of circuits, and creates the problem that efficient mass production is difficult so that the manufacturing cost of the head chip 2 and the line chip 1 is high.
In view of the above problems with the related art, this invention has the object of providing a line head ink-jet printer having lower manufacturing costs because of more efficient mass production due to a simple head chip configuration, and further having high resolution and image quality along with reduced power consumption.
To attain the above objectives, according to one aspect of the present invention, there is provided an ink-jet printer emitting droplets of ink arriving as ink dots forming images and letters recorded onto a recording medium from a line head having a plurality of nozzles arrayed in the width direction of the recording medium which is almost perpendicular to the feed direction of the recording medium comprising head chips having a specified number of nozzles and a drive circuit to drive each nozzle, wherein a plurality of the head chips are arrayed in the width direction thereof to form the line head so that the nozzles each head chip has and the nozzles the neighboring head chips have are not arrayed in the feed direction of the recording medium.
To also attain the above objectives, according to another aspect of the present invention, there is provided an ink-jet printer, wherein the nozzles each head chip has are sequentially time-series driven by separate driving, and the number of the nozzles each head chip has is an integer multiple of the number of phases for the separate driving of the nozzles.
To also attain the above objectives, according to still another aspect of the present invention, there is provided an ink-jet printer emitting droplets of ink arriving as ink dots forming images and letters recorded onto a recording medium from a line head having a plurality of nozzles arrayed in the width direction of the recording medium which is almost perpendicular to the feed direction of the recording medium comprising head chips having a specified number of nozzles and a drive circuit to drive each nozzle, in which a plurality of the head chips are arrayed in the width direction thereof to form the line head so that the nozzles each head chip has and part of the nozzles the neighboring head chips have are arrayed in the feed direction of the recording medium.
To also attain the above objectives, according to still another aspect of the present invention, there is provided an ink-jet printer, wherein said nozzles each head chip has are sequentially time-series driven by separate driving, and the number of the nozzles each head chip has is the number of the part of the nozzles the neighboring head chips have and the number of nozzles arrayed in the feed direction of the recording medium added to the integer multiple of the number of phases for the separate driving of the nozzles.
In the above structure, the nozzles for each head chip are set as an integer multiple of the number of phases for separate driving of the nozzles or set as this figure added with the number of over lapping nozzles, so that when a plurality of head chips are arrayed by tiling to comprise a line head, the block of time-shared driven nozzles are matched in a coordinated manner with the head chips.
Therefore, by arraying a plurality of head chips each having a small number of nozzles, a line head can be configured by so-called tiling, so that along with obtaining high image resolution and high image quality by a higher dot placement density, the power consumption can be reduced by time-division driving of the nozzles.
Further, the structure of the drive circuit containing the drive elements for driving each nozzle is the same for each head chip so that a line head can be comprised by arraying a plurality of head chips each containing an identical drive circuit, and since only one type of head chip is being produced, efficient mass production can be achieved.